Protein fortification of acidic foods having a pH in the range of 2 to 6 is complicated by the unavailability of protein exhibiting satisfactory nutritional and taste characteristics. Oleaginous proteins, especially soy protein, when altered to be acid soluble, are characterized as having undesirable taste characteristics variously described as beany and bitter. The objectionable flavor is especially noticeable in acidic beverages that contain an insufficient number of other ingredients to mask the strong flavor at the protein levels of 2% to 8% or higher.
Hydrolysis of seed protein by the action of proteolytic enzymes is already a well known procedure, resulting in a water soluble product that may remain soluble or partially soluble under acidic conditions. Known processes for enzyme digestion are described in U.S. Pat. No. 3,814,816, U.S. Pat. No. 3,830,942, U.S. Pat. No. 3,843,802 and U.S. Pat. No. 3,846,560.
According to the conventional procedure, protein is isolated from the seed in a water slurry. The proteolytic enzyme is added, and the pH of the slurry is adjusted to optimize the reaction conditions relative to the specific enzyme employed. The slurry may be heated prior to the addition of the enzyme as well as during enzyme digestion.
The polypeptide mixture produced from enzyme hydrolysis is water soluble at acid or neutral pH, but has a stronger flavor than the original isolated protein. Consequently, it would be desirable to decrease the strong or bitter flavors and yet retain acid solubility.